New York City health officials are continuing to investigate a cluster of Legionnaires’ disease, a serious bacterial lung infection, where the number of cases has risen to 73, including three deaths.

The cases are most likely linked to a cooling tower in central Harlem, health officials said. More than 60 people have fallen ill, including three people who have died, from Legionnaires’ disease in New York City over the past several weeks, according to the city’s health department.

The disease is a type of pneumonia caused by the bacteria Legionella, which grow in warm water and can spread in building water systems such as showerheads.